[PATCH v14 02/18] memcg: consolidate callers of memcg_cache_id

Vladimir Davydov
2013-12-16T12:22:06Z

From: Glauber Costa <glommer@openvz.org>

Each caller of memcg_cache_id ends up sanitizing its parameters in its own way.
Now that the memcg_cache_id itself is more robust, we can consolidate this.

Also, as suggested by Michal, a special helper memcg_cache_idx is used when the
result is expected to be used directly as an array index to make sure we never
access in a negative index.

Signed-off-by: Glauber Costa <glommer@openvz.org>
Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
mm/memcontrol.c | 49 +++++++++++++++++++++++++++++--------------------
1 file changed, 29 insertions(+), 20 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3408852..35a367c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2963,6 +2963,30 @@ static inline bool memcg_can_account_kmem(struct mem_cgroup *memcg)
}

/*
+ * helper for acessing a memcg's index. It will be used as an index in the
+ * child cache array in kmem_cache, and also to derive its name. This function
+ * will return -1 when this is not a kmem-limited memcg.
+ */
+int memcg_cache_id(struct mem_cgroup *memcg)
+{
+ if (!memcg || !memcg_can_account_kmem(memcg))
+ return -1;
+ return memcg->kmemcg_id;
+}
+
+/*
+ * This helper around memcg_cache_id is not intented for use outside memcg
+ * core. It is meant for places where the cache id is used directly as an array
+ * index
+ */
+static int memcg_cache_idx(struct mem_cgroup *memcg)
+{
+ int ret = memcg_cache_id(memcg);
+ BUG_ON(ret < 0);
+ return ret;
+}
+
+/*
* This is a bit cumbersome, but it is rarely used and avoids a backpointer
* in the memcg_cache_params struct.
*/
@@ -2972,7 +2996,7 @@ static struct kmem_cache *memcg_params_to_cache(struct memcg_cache_params *p)

VM_BUG_ON(p->is_root_cache);
cachep = p->root_cache;
- return cache_from_memcg_idx(cachep, memcg_cache_id(p->memcg));
+ return cache_from_memcg_idx(cachep, memcg_cache_idx(p->memcg));
}

#ifdef CONFIG_SLABINFO
@@ -3070,18 +3094,6 @@ void memcg_cache_list_add(struct mem_cgroup *memcg, struct kmem_cache *cachep)
}

/*
- * helper for acessing a memcg's index. It will be used as an index in the
- * child cache array in kmem_cache, and also to derive its name. This function
- * will return -1 when this is not a kmem-limited memcg.
- */
-int memcg_cache_id(struct mem_cgroup *memcg)
-{
- if (!memcg || !memcg_can_account_kmem(memcg))
- return -1;
- return memcg->kmemcg_id;
-}
-
-/*
* This ends up being protected by the set_limit mutex, during normal
* operation, because that is its main call site.
*
@@ -3243,7 +3255,7 @@ void memcg_release_cache(struct kmem_cache *s)
goto out;

memcg = s->memcg_params->memcg;
- id = memcg_cache_id(memcg);
+ id = memcg_cache_idx(memcg);

root = s->memcg_params->root_cache;
root->memcg_params->memcg_caches[id] = NULL;
@@ -3406,9 +3418,7 @@ static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
struct kmem_cache *new_cachep;
int idx;

- BUG_ON(!memcg_can_account_kmem(memcg));
-
- idx = memcg_cache_id(memcg);
+ idx = memcg_cache_idx(memcg);

mutex_lock(&memcg_cache_mutex);
new_cachep = cache_from_memcg_idx(cachep, idx);
@@ -3581,10 +3591,9 @@ struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep,
rcu_read_lock();
memcg = mem_cgroup_from_task(rcu_dereference(current->mm->owner));

- if (!memcg_can_account_kmem(memcg))
- goto out;
-
idx = memcg_cache_id(memcg);
+ if (idx < 0)
+ goto out;

/*
* barrier to mare sure we're always seeing the up to date value. The
--
1.7.10.4